Intrauterine devices seem to be an effective method of emergency contraception with a failure rate of less than one per thousand, according to a meta-analysis.

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Unintended pregnancy is a signiﬁcant problem, with at least 36% of pregnancies worldwide and nearly half of pregnancies in the U.S. being unintended.

This study indicates that intrauterine devices are a highly effective method of contraception after unprotected intercourse when inserted post-coitally.

Intrauterine devices (IUDs) seem to be an effective method of emergency contraception, with a failure rate of less than one per thousand, according to a meta-analysis.

In a review of 35 years of data in which IUDs were inserted after unprotected intercourse, 99.86% of overall women did not become pregnant, reported Kelly Cleland, a research scientist at Princeton University in New Jersey, and colleagues in Human Reproduction.

Unintended pregnancy is a signiﬁcant problem, with at least 36% of pregnancies worldwide and nearly half of pregnancies in the U.S. being unintended, the authors noted in their introduction. Emergency contraception is a popular method for preventing unwanted pregnancy, with oral methods such as levonorgestrel (Plan B) and ulipristal acetate (Ella or EllaOne), among the leading medications used.

Although IUDs are another option, negative experiences with the Dalkon Shield in the 1970s led to years of low IUD use, the authors pointed out. But one of the major advantages of copper IUDs is that after placement for emergency contraception, the device can be left in and will continue to prevent pregnancy for at least a decade.

Cleland's group conducted a systematic review intended to provide a current estimate of the efficacy of IUDs as emergency contraception. They found 274 articles, in English and Chinese, published by August 2011 but narrowed the list to 42 studies published from 1979 to 2011.

The authors noted that they included studies published in Chinese because, according to China's family planning commission, 53% of married women surveyed in 2009 who used contraception opted for an IUD.

"IUD use is higher in China than in the world overall," they explained, and of the 42 studies analyzed, 17 were conducted in that country.

Nearly all of the IUDs included in the studies were copper-bearing, and in nearly three-fourths of cases (74%) the current standard protocol of inserting the IUD within 5 days of unprotected sex was used.

Among more than 7,000 postcoital IUD insertions, there were 10 pregnancies, for an overall failure rate of 0.14% (95% CI 0.08% to 0.25%).

One study, conducted in Egypt, turned in the highest number of pregnancies at four among 200 enrollees (2% pregnancy rate). The researchers called this failure rate "surprisingly high, and significantly higher than the rate in all other countries" (P=0.0001).

But they pointed out that the Egyptian study was a randomized, controlled trial with a non-treatment arm (expectant management) and that the investigators intentionally selected women who were at a greater risk of pregnancy.

If data from this "outlier" study is removed from the meta-analysis, then the overall failure rate for IUDs would be 0.09% (95% CI 0.04% to 0.19%).

The copper IUD could prove to be the most effective means of emergency contraception, followed by ulipristal acetate (failure rate of about 1.4%) and levonorgestrel (failure rate of about 2 to 3%), the authors wrote.

Finally, the group mentioned some barriers to a greater use of IUDs, including a lack of interest among healthcare providers. A study of contraceptive providers in California showed that 85% of clinicians never suggested the IUD for emergency contraception and 93% required at least two visits for an insertion (Obstet Gynecol 2012; 119: 220-226).

Limitations of the analysis included the fact that the studies evaluated did not provide enough detail on the day of insertion, so the investigators could not take into consideration the length of delay between intercourse and insertion of the IUD. Also, the authors were not able to provide estimates of the IUD's efficacy as it related to individual pregnancy risk, the cycle day on which intercourse occurred, or IUD type, again because the studies that were evaluated did not provide enough data on these variables.

Still, they concluded that IUDs could be routinely promoted as an emergency contraceptive option for some women.

A related study presented this week at the American College of Obstetricians and Gynecologists meeting found that doctors underestimated the pain their patients felt during IUD insertion.

One co-author received a grant from the Eunice Kennedy Shriver National Institute of Child Health and Development.